1. Field
The disclosed concept relates generally to machinery and, more particularly, to can decorator machines and methods for decorating cans used in the food and beverage packaging industries. The disclosed concept also relates to ink station assemblies for can decorator machines.
2. Background Information
High speed continuous motion machines for decorating cans, commonly referred to as can decorator machines or simply can decorators, are generally well known.
FIG. 1 shows a can decorator 2 of the type disclosed, for example, in commonly assigned U.S. Pat. No. 5,337,659, which is incorporated herein by reference. The can decorator 2 includes an infeed conveyor 15, which receives cans 16 from a can supply (not shown) and directs them to arcuate cradles or pockets 17 along the periphery of spaced parallel rings secured to a pocket wheel 12. The pocket wheel 12 is fixedly secured to a continuously rotating mandrel carrier wheel 18, which in turn is keyed to a continuously rotating horizontal drive shaft 19. Horizontal spindles or mandrels (not shown), each being pivotable about its own axis, are mounted to the mandrel carrier wheel 18 adjacent its periphery. Downstream from the infeed conveyor 15, each spindle or mandrel is in closely spaced axial alignment with an individual pocket 17, and undecorated cans 16 are transferred from the pockets 17 to the mandrels by wiping against a stationary arm 42, which is angled inwardly in the downstream direction so as to function as a cam that drives the can 16 toward the corresponding mandrel. Suction applied through an axial passage of the mandrel draws the can 16 to a final seated position on the mandrel.
While mounted on the mandrels, the cans 16 are decorated by being brought into engagement with a blanket (e.g., without limitation, a replaceable adhesive-backed piece of rubber) that is adhered to a blanket segment 21 of the multicolor printing unit indicated generally by reference numeral 22. Thereafter, and while still mounted on the mandrels, the outside of each decorated can 16 is coated with a protective film of varnish applied by engagement with the periphery of an applicating roll (not shown) rotating on a shaft 23 in the overvarnish unit indicated generally by reference numeral 24. Cans 16 with decorations and protective coatings thereon are then transferred from the mandrels to suction cups (not shown) mounted adjacent the periphery of a transfer wheel (not shown) rotating on a shaft 28 of a transfer unit 27. From the transfer unit 27 the cans 16 are deposited on generally horizontal pins 29 carried by a chain-type output conveyor 30, which carries the cans 16 through a curing oven (not shown).
While moving toward engagement with an undecorated can 16, the blanket engages a plurality of printing cylinders 31, each of which is associated with an individual ink station assembly 32 (six ink station assemblies 32 are shown in the example of FIG. 1). Each ink station assembly 32 includes a plurality of form rolls 33, 34 and other rolls (e.g., without limitation, roll 35 shown in simplified form in hidden line drawing in FIG. 1; see also FIG. 5) that produce a controlled film of ink, which is applied to a printing cylinder 31. Typically, each assembly 32 provides a different color ink and each printing cylinder 31 applies a different image segment to the blanket. All of these image segments combine to produce the same main image. This main image is then transferred to undecorated cans 16.
When decorating metal, it is important to supply the printing cylinder 31 with as consistent of an ink film thickness, as possible, in order for the printing plate to impart a clear and consistent image to the printing blanket 21 and ultimately to the final printed substrate (e.g., can 16). Inconsistencies in the ink film can result in variable color density across the printed image, as well as present the possibility of “starvation ghosting” of the image, wherein a lighter duplicate version or copy of the image is undesirably applied to the can 16 in addition to the main image. Prior proposals for solving the problem of ink film consistency and related issues such as starvation ghosting, have included such approaches as adding more form rolls, changing form roll diameters, each of the form rolls having a different diameter all of which are less than the diameter of the printing cylinder, adding a number of rider rolls and/or oscillating rider rolls on one or more of the form rolls, and/or variation of the axial cycle rates of the oscillating roll(s).
There is, therefore, room for improvement in can decorating machines and methods, and in ink station assemblies.